Brain Pathology Case of the Month - January 2008

DIAGNOSIS: Masson's tumor (papillary endothelial hyperplasia)

DISCUSSION:

Masson's tumor was first described by Pierre Masson in 1923 as a lesion in an ulcerated hemorrhoidal vein and in the 80 years since, has appeared in the literature under a variety of names, including Masson's tumor, Masson's hemangioma, Masson's pseudoangiosarcoma, Masson's vegetant intravascular hemangioendothelioma (MVH), intravascular papillary endothelial hyperplasia, and reactive papillary endothelial hyperplasia (1). Although the original author considered the lesion to be neoplastic, MVH is now recognized to be an unusual and overly exuberant pattern of organization within a venous or arterial thrombus or hemangioma (2). Masson tumor's (MVH) is a benign condition that must be distinguished by the pathologist from epithelioid hemangioendothelioma, Kaposi's sarcoma, and malignant angiosarcoma (3), since the lesion is usually curable by surgical excision alone (1).

Microscopically, short, blunted papillary projections with a hyalinized core are associated with thrombotic or clot material and are covered by a single layer of plump endothelial cells that lack anaplasia, pleomorphism, or significantly elevated mitotic activity, unlike angiosarcomas. As in this case, the frond-like structures may fuse into bands of collagenous tissue, occasionally containing inflammatory cells, hemosiderin, or even extramedullary hematopoiesis (4, 5). It does not show the HHV-8 association seen with Kaposi's sarcoma.

In systemic sites, three types of MVH have been described: a primary form arising within a normal blood vessel (usually a vein), a secondary form developing in a pre-existing vascular malformation (usually a cavernous hemangioma or pyogenic granuloma), and an extravascular form (sometimes arising in an organizing hematoma) (1). In a recent review of reported central nervous system examples, seven of 13 cases were classified as secondary forms (1), but this may be an underestimate. Pre-existing cavernous angiomas have been suspected in some cases (7) and we especially suspected a cavernous angioma in our case. While most cavernous angiomas are sporadic lesions, Hispanic-Americans are known to have a higher incidence of familial, autosomal dominant forms due to a C1363T mutation in the KRIT1 gene on the long arm of chromosome 7. Many of these affected Hispanic-Americans immigrated to the southwestern USA from northern Mexico and share an identical founder mutation that has not been found among persons with cavernous angiomas who reside in Mexico (8). Affected Hispanic individuals in the Southwestern USA frequently share a common ancestor (9). In our patient, despite his heritage and residence in an area of our state with many affected CCM patients, no underlying cavernous angioma could be recognized by neuroimaging, histological examination, or genetic testing.